First to check on a couple things... did screw in chokes come with your shotgun? I would try those first. Also, what kind of pattern are you seeking? Some try to concentrate shot into the head and neck, which is understandable given that you are dealing with very edible game. Full chokes should help with that. I have seen some recommendations for a modified choke. Keep in mind that will open your pattern up into more bird. If you go down to improved cyinder, wider still.

I hear hunters bragging up Briley chokes although I have not personally tried one. They also build for Franchi.